Flavodoxins have been shown to be low molecular weight models for which the properties and behavior of higher molecular weight flavoenzymes may be readily studied. The reaction rates of biologically important chemical reactions can be accelerated by 8 to 14 orders of magnitude by the presence of enzymes. The origins of this catalytic enhancement effect is hardly understood in any enzyme. The flavoenzymes offer a set of enzymes found in nearly every basic electron transferring system in nearly all living organisms. The malfunction of flavoenzymes has been implicated in many metabolic and neurological disorders in humans. The amino acid sequences for several flavodoxins and the three-dimensional structures for two have been determined. Thus, it is now possible to explore the contributions of specific amino acid sidechains to the catalytic process in flavodoxins. This study is directed towards the chemical modification of two flavodoxins, each chosen as a representative of the two flavodoxin subclasses. These subclasses appear to differ by the nature of the two amino acid sidechains which sandwich the flavin ring to the apoenzyme. The number and location of these "specific" chemical modifications are being determined. A number of the physical characteristics of the modified flavodoxin are then determined. These results are to be correlated with quantum mechanical calculations of the enzyme active site.